This project will examine the impact of the states of alertness (wakefulness, nonrapid eye movement (NREM), and rapid eye movement (REM) sleep), inactivity, and circadian rhythms in elderly who do not have sleep-related respiratory disturbances. With the shift from one state of alertness to another there is a shift in the balance of the autonomic nervous system (ANS), which modulates the activity of many internal organs. A dysfunction of either the ANS or a specific organ may increase physical decline and the risk for early mortality. The aging process appears to disrupt the ANS modulation; resulting dysfunctions may be more apparent and more detrimental in a specific state of alertness. We will study nocturnal ventricular ectopy, frequently associated with coronary artery disease, in elderly subjects who will undergo a 144-hour protocol involving a reversal of day/night sleep patterns. Our aim is to determine if sleep states, sleep stages, inactivity, the supine position, and circadian rhythms during the night increase the risk of further dysfunction. With the sleep-reversal protocol, we will dissociate the sleep-related variables from the impact of circadian rhythms to determine which variables pose the greatest risk.